Drinking flask



FIG. 1 is a perspective view of a drinking flask showing the new design;

FIG. 2 is a left side elevational view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a bottom view thereof;

FIG. 5 is a rear view thereof;

FIG. 6 is a right side elevational view thereof;

FIG. 7 is a front view thereof; and,

FIG. 8 is a vertical cross-sectional view thereof. 

The ornamental design for a drinking flask, as shown. 